1. Field of the Invention
The present invention relates to an organic EL display device, and more particularly, to a manufacturing method of a highly reliable organic EL display device which is capable of suppressing generation of a dark spot especially caused by moisture.
2. Description of the Related Art
Generally, an organic EL display device has an organic EL layer interposed between a pixel electrode (lower electrode) and an upper electrode. The fixed voltage is applied to the upper electrode and the data signal voltage is applied to the lower electrode to control emission of the organic EL layer so as to form the image. The data signal voltage is supplied to the lower electrode via a thin film transistor (TFT). The organic EL display device has two types: a bottom emission type for taking the light emitted from the organic EL layer along the direction of the glass substrate having the organic EL layer formed thereon; and a top emission type for taking the light along the direction opposite the glass substrate having the organic EL layer formed thereon.
The water contained in the organic EL material for forming the organic EL display device may deteriorate the emission property. The position with the deteriorated emission property due to the water no longer emits the light after a prolonged operation of the device. Such position becomes the dark spot on the display region, and grows over time to cause failure of the image. Such phenomenon as the edge growth having the non-luminous region increased around the pixel may also occur under the influence of the water.
In order to prevent generation or growth of the dark spot, it is necessary to prevent intrusion of water into the organic EL display device, or remove the intruded water. For this, the element substrate with the organic EL layer is sealed with the seal substrate via a seal disposed in the circumference thereof to prevent external intrusion of water into the organic EL display device. The inner sealed space is filled with such inert gas as N2. Meanwhile, the desiccant is disposed inside the organic EL display device for dehumidifying the inner space thereof. The aforementioned organic EL display device is of hollow seal type.
The hollow seal type organic EL display device has problems of difficulty in adjustment of the gap between the element substrate and the seal substrate, difficulty in adjustment of the inside of the sealed portion, contamination of the organic EL material by the gas discharged from the sealing agent when sealing, and the low throughput.
The technique for protecting the organic EL material from water using the resin sheet with the predetermined film thickness interposed between the element substrate and the seal substrate is referred to as the solid sealing, which is used for solving the problems with respect to the hollow sealing.
JP-A No. 2004-139977 discloses the example of the solid sealing. FIGS. 12A to 12D show the structure disclosed in JP-A No. 2004-139977. Referring to FIGS. 12A to 12D, a light curable resin 104 on a light transmissive film 101 is applied to an element substrate 10 with an organic EL layer 22 using a pressure roller 105 heated at 80° C. Then the UV light is irradiated to cure the light curable resin 104 to peel the light transmissive film 101, thus providing the organic EL display device sealed with the light curable resin. The structure for covering the organic EL element with the silicon nitride film if needed is disclosed as well.
The article in “Nikkei Electronics 2007” Sasaki Shinya, No. 960, pp. 10-11, Sep. 10, 2007 discloses the following technique as shown in FIGS. 13A to 13E for sealing the organic EL display device. Specifically, a resin film 107 is applied to the portion of the seal substrate 40 corresponding to the organic EL element 103, and the seal agent 108 is applied around the resin film 107. Then the resin film 107 is used for bonding the seal substrate 40 having the seal agent 108 formed thereon, and the electrode substrate 10 having the organic EL element 103 formed thereon. The UV light is irradiated from the seal substrate 40 to conduct the thermal processing at the temperature in the range from 80° C. to 100° C. for curing the seal agent 108. Simultaneously, the resin film 107 with fluidity spreads over the space defined by the seal substrate 40, the element substrate 10, and the seal agent 108 to fill the defined space. The thus formed material is cut to have the respective organic EL display panels.
JP-A No. 2006-66364 discloses the structure for forming plural display elements on the mother panel, forming the sealing films for the respective display elements, and removing the protective film from the terminal by the laser abrasion. FIGS. 14A and 14B represents the structure disclosed in JP-A No. 2006-66364, in which plural display elements each with the light emitting portion 207 and the terminal portion 209 are formed on the mother panel 206 so as to be coated with the protective film 208. Then the protective film 208 at the portion 210 of the terminal portion 209 is eliminated by the laser abrasion to form the opening 210.
JP-A No. 2004-139977 discloses the structure for protecting the organic EL layer by applying the resin sheet to the respective organic EL display devices. The problem which occurs when the resin sheet is used for coating the plural organic EL panels formed on the mother panel to be separated is not described in the document.
In the Sasaki, it is important to balance the height of the resin film with that of the seal agent. If such balance is lost, the life of the organic EL display device may be shortened. The thermal process after sealing renders fluidity to the resin film to spread, which increases the pressure inside the organic EL display device to form the leak path leading to the outside, thus shortening the life of the organic EL display device. The influence of degasifying when the seal agent is cured to the resin sheet may deteriorate the sealing capability.
In the technology disclosed in JP-A No. 2006-66364, after applying the single resin sheet to the mother panel on which the plural organic EL display panels are formed, the opening is formed for removing the resin sheet for each terminal of the respective organic EL panels, resulting in low production capacity. The number of facilities has to be increased to expand the output, thus increasing the manufacturing cost. The use of high energy laser light rays for abrasion may cause the risk of damaging the connector terminal. The use of the laser to remove the resin sheet may also cause the risk of leaving the residue on the terminal.